Tanning



Patented Mar. 21, 1939 UNITED STATES TANNING Martin E. Cupery and David M. McQueen, Wil' mington, Del., assignors'to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application February 1, 1938, Serial No. 188,055

6 Claims.

This invention relates to the preparation of hides for tanning and is more particularly directed t0 compositions and processes wherein sulfamic acid or ammonium sulfamate is employed for the treatment of limed, unhaired hides.

In the course of the manufacture of leather from hides it is customary to treat the hides with lime and sodium sulfide to remove hair and epidermis. When hides are thus limedin the usual Way with hydrated lime and sodium sulfide, hair on the hide is removed and bits of flesh and similar detritus are loosened.

Now we have found that limed hides may advantageously be treated in solutions of sulfamic acid or ammonium sulfamate. Limed hides even after washing contain residual calcium compounds and should be given a deliming or socalled bating or cleaning treatment. Sulfamic acid solutions or solutions of ammonium sulfamate effectively serve to delime or bate the hides and they are-particularly advantageous because calcium sulfamate which is formed is highly water soluble. The treatment with sulfamic acid or ammonium sulfamate thus leads to the formation of an easily extractable salt and the calcium can readily be removed from the leather.

Another operation ordinarily performed on hides prior to tanning is that of pickling the hides with an acid after they have been delimed and bated. Sulfamic acid solutions can be used to effect pickling of the hides. It will be seen, therefore, that when a limed hide is placed directly in a sulfamic acid solution according to the processes of our invention, it may if desired be at once delimed and pickled. sulfamic acid appears to have a lower hydrolytic effect on-proteins than other acids such as hydrochloric acid, and with sulfamic acid the damage to hides by reason of acid swelling is minimized.

The concentration of sulfamic acid solution or solution of ammonium sulfamate will be adjusted according to considerations already known to the art. In the deliming operation sulfamic acid or ammonium sulfamate' should be present only in an amount suflicient to remove the calcium residues from the hides to the desired extent. As is the customary practice, the pH of the hide will be brought to a minimum of about pH 8.2.

When sulfamic acid is used both for deliming and pickling the concentration of sulfamic acid in the pickling operation will need to be increased. The exact amount of -sulfamic acid used will depend upon the degree of pickling desired which in turn will depend upon the. type of tanning operation which is to be used and acidity of the pickle solutions will ordinarily becarried to a minimum pH not substantially lower than about pH 1.5.

It will be understood that when using sulfamic acid it is generally preferable to use a low acidity for deliming and then to increase the acidity for pickling as indicated since if the deliming is effected in the concentration of sulfamic acid finally to be used for pickling, there may immediately be effected a severe surface plumping with possible ineffective removal of the lime and with possible damage to the hide. However, if desired, a relatively high acidity may be maintained throughout the process using sodium chloride to restrain undesirable surface plumping.

When the process is conducted in two stages it may also be found desirable under some circumstances to interpose a washing step in the process to clean off the hide after deliming but before the pickling proper is begun.

The use of sulfamic acid in deliming will be found particularly advantageous in conjunction with the use of sulfamic acid in pickling as herein described, but it will be understood that hides delimed with sulfamic acid may then, if desired, be pickled by any suitable process.

When ammonium sulfamate is used for deliming, the pickling may advantageously be effected by the addition of the required amount of sulfamic acid after completion of the deliming operation. It will be apparent that any customary pickling operation may be used with the novel deliming processes of our invention.

The processes of our invention may be better understood by reference to the following illustratlve examples:

Example 1 Calf skins which had been limed and from which hair and flesh had been removed were treated with a solution of sulfamic acid, the quantity of sulfamic acid being one and one-half per cent by weight of sulfamic acid based on the hide weight. After agitation for one hour there was no alkalinity to phenolphthaiein apparent and thehides were permitted to stand for twenty-four hours to assure of even and thorough deliming.

The concentration and content of the sulfamic acid solution was then varied so that the solution contained upon a basis of hide weight three percent by weight of sulfamic acid, forty-eight per cent by weight sodium chloride, and four hundred per cent by weight of water. The pickling operation was permitted to continue for twenty-four hours at the end oi which time the pH was noted as pH 1.9.

The delimed pickled hides thus obtained were in excellent condition for subsequent tanning in a chrome tanning process.

Example 2 A bated steer hide delimed with ammonium chloride was pickled with a sulfamic acid solution containing four per cent by weight of sulfamic acid, twenty per cent by weight of sodium chloride, and four hundred per cent of water all based upon the weight oi. hide. Even with the diminished quantity of sodium chloride of this example, there was no acid swelling of the hides and after twenty-four hours the .hides were pickled and were in a condition toserve as a raw material for a chrome tanning, an alum tanning or other such tannage for which pickled stocks may advantageously be used.

Example 3 Calf skins which had been limed, unhaired and from which the flesh had been removed were treated with an aqueous solution containing one per cent by weight of ammonium sulfamate based upon the weight of hide treated. After one hour and ten minutes bating was complete, the pH of the hide remaining substantially unchanged over a further test period. The hides were very satisfactorily delimed and were in good condition for a subsequent pickling or tanning operation.

It will be understood that the term hides has been used herein in a generic sense to include all skins and hides amenable to deliming and pickling procedures rather than in the strict sense of the term hide as referring to heavy skins specifically as has sometimes been the practice.

While we have shown certain illustrative processes herein, it will be understood that one skilled in .the art without departing from the spirit of our invention may readily employ sulfamic acid or ammonium sulfamate for deliniing hides in a number 01' ways.

We claim: 7 I

1. In a process for the treatment of limed hides to prepare them for tanning, the steps comprising treating a hide with an acidic material selected i'rom the group consisting of sulfamic acid and ammonium sulfamate.

2. In a process for the treatment of limed hides to prepare them for tanning, the step comprising treating a hide with suliamic acid.

3. In a process for the treatment of limed hides to delime them, the step comprising subjecting a hide to a solution of a material selected from the group consisting of sulfamic acid and am.- monium sulfamate, the material being present in an amount only slightly inexcess of that required to remove the lime from the hide.

4. In a process for the treatment of limed hides to delime them, the step comprising subjecting 9. hide to a solution of ammonium sulfamate, the sulfamate being present in an amount only slightly in excess of that required to remove the lime from the hide.

5. In a process for the treatment of limed hides to prepare them for tanning, the step comprising treating a hide with sulfamic acid to delime the hide and then treating the delimed hide 35 with sulfamic acid to pickle the hide.

6. In a process for the treatment of hides to pickle them prior to tanning, the step compris-- ing treating 9. hide with sulfamic acid. 

